The long-term goal of our research is to determine if the polysaccharide composition of plant cell walls can be altered in predictable ways without negatively affecting plant growth and viability. If such changes are possible, plant cell walls will be produced that are a better source of biomass for production of fuel and other chemicals than present cell walls. The specific goal of this project is to determine the chemical structure of purified cell wall pectic polysaccharides of Lemna minor. The pectic polysaccharides will be characterized: (i) by establishing their homogeneity with respect to Mw, sugar composition, and degree of methyl esterification and (ii) by determining the position of the covalent linkages between sugar residues. The basic structure of each polysaccharides must be determined before their biosynthesis and the control of their biosynthesis can be understood. The biosynthetic pathway and their control must be known before mutant plants with altered cell wall polysaccharide compositions can be produced. Mass spectrometry analyses were needed to identify sugar residues and to determine the proportion of galactose and galacturonic acid (reduced to galactose with NaB2H4) in polysaccharides. The latter was done by selective ion monitoring.